Specifications

HP Virtual Connect for Cisco Network Administrators (version 1.2x) page 14
configured on all the uplinks associated with the vNet, the server connectivity should be restored in
under five seconds. If the previous active uplink has it’s link restored, VC will automatically failback
to it. As long as the external Cisco switch port has been properly configured by enabling PortFast,
connectivity to servers should be restored in under five seconds.
Virtual Connect uses a mechanism called “Fast MAC Cache Failover” to proactively update the
CAM tables on the upstream Cisco switch ports. Whenever a vNet fails over or fails back from one
uplink to another, this mechanism will transmit a single frame on the new active uplink for every
server MAC address that is active within the VC domain. Fast MAC Cache Failover enables VC to
immediately update the external Cisco infrastructure with the new location of the active VC uplink
for a particular vNet. Fast MAC Cache Failover is very similar to the CAM table update process used
by Link-State Tracking on Cisco switches.
VC Uplink Load Balancing
Virtual Connect provides load balancing (and fault tolerance) across multiple VC uplinks on the
same physical VC-Enet module by means of IEEE 802.3ad port trunking or port channeling
(EtherChannel) using the Link Aggregation Control Protocol (LACP). The vNet (or Shared Uplink Set)
must have its “connection mode” set to “auto” (default) and not in mode “failover”.
If the external switch is a Cisco switch, the ports in the EtherChannel must be set to either “mode
active” or “mode passive”. Both of these modes on the Cisco switch enable the use of 802.3ad
LACP (the only port channeling protocol VC supports). VC does not support port channeling with
Cisco switch ports when set to “mode on”, “mode desirable” or “mode auto”.
Note:
An EtherChannel can only be formed between VC and a Cisco switch if the VC vNet is set to
connection mode “Auto” and the Cisco switch’s channel-group is set to either “mode active” or
“mode passive”.
There are four types of scenarios for port trunking\channeling with Virtual Connect Uplink Ports:
• Same VC Module, Same External Switch, Same Port Channel Group
When VC uplinks from the same physical VC-Enet module are assigned to the same vNet (or
Shared Uplink Set) and are connected to ports on the same external Cisco switch that are
assigned to the same port channel group and have the LACP protocol enabled, then VC will
automatically form a single port channel.
• Same VC Module, Same External Switch, Different Port Channel Groups
When VC uplinks from the same physical VC-Enet module are assigned to the same vNet (or
Shared Uplink Set) and are connected to ports on the same external Cisco switch that are
assigned to different port channel groups and have the LACP protocol enabled, then VC
may automatically form more than one port channel.
• Same VC Module, Different External Switches
When VC uplinks from the same physical VC-Enet module are assigned to the same vNet (or
Shared Uplink Set) and are connected to ports on different external Cisco switches that are
assigned to port channel groups and have the LACP protocol enabled, then VC may
automatically form more than one port channel.
• Different VC Module, Same or Different External Switches
When VC uplinks from different physical VC-Enet modules are assigned to the same vNet (or
Shared Uplink Set) and are connected to ports on the same (or different) external Cisco
switch that are assigned to a port channel group and have the LACP protocol enabled,
then VC may automatically form more than one port channel.
As described above, VC’s default behavior (connection mode ‘auto’) for a vNet is to attempt to
negotiate a port channel (EtherChannel) using 802.3ad Link Aggregation Control Protocol (LACP). If
LACP negotiation is successful for one or more sets of VC uplink ports, a port channel is formed